| 摘要 |
1,044,992. Lasers; pulse modulation systems. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 14, 1964 [May 17, 1963], No. 20096/64. Headings H3B and H4L. A pulse modulated carrier wave transmitter comprises a semi-conductor laser the input current of which is pulse-modulated in accordance with the amplitude of an input signal. An audio input signal applied to terminal 30 and amplified by transistor T1 is applied to the base of transistor T2 so that the current on line 34 is modulated in accordance with the audiomodulated input signal. The capacitors of L-C delay line 36 are charged by the modulated current on line 34 until the voltage across PNPN diode 40 is sufficient to cause this diode to break down and a pulse to be passed to semi-conductor laser diode 42 so as to switch the diode to its lasing condition. At the end of the output pulse on line 41 the PNPN diode 40 is switched back to its high impedance state by feeding a positive pulse to the base of transistor T2 to reduce the emitter/collector current of transistor T1 to zero and hence also the current flowing through diode 40. After restoration of the switch 40 the capacitors of delay line 36 begin to recharge through the transistor T2 so that a PFM signal corresponding in information content to the audio modulated input signal is generated on line 41. The radiation output from the laser is thus an optical PFM signal embodying the information carried on the audio input signal. The amplitude characteristics of the input signal correspond to the pulse repetition rate of the PFM signal and frequency characteristics of the input signal are embodied as the rate of change of the pulse repetition rate. The laser may be a gallium-arsenide diode.
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